1. Field of the Invention
The present invention relates to a Vertical Cavity Surface Emitting Laser (VCSEL) that emits a laser light from the top face and a method of manufacturing the same.
2. Description of the Related Art
A VCSEL emits light in the direction orthogonal to a substrate differently from the existing edge-emitting laser diodes. In the VCSEL, many devices can be arranged in a state of a two-dimensional array on the same substrate. Therefore, the VCSEL has recently attracted attention as a light source for a digital copy machine or a printer.
In the past, in the foregoing type of VCSEL, a pair of multilayer film reflectors was formed over the semiconductor substrate, and an active layer becoming a light emitting region was provided between the pair of multilayer film reflectors. Between one of the multilayer film reflectors and the active layer, to improve efficiency of current injection into the active layer and lower the threshold value current, a current confinement layer having a structure in which a current injection region was confined is provided. Further, a lower electrode was provided on the bottom face side, and an upper electrode was provided on the top face side. The upper electrode was provided with an aperture to emit laser light. In the VCSEL, a current was confined by the current confinement layer injected into the active layer where light is emitted. While the emitted light repeated the reflection between the pair of multilayer film reflectors, the light was emitted as laser light from the aperture of the upper electrode.
In general, the foregoing VCSEL has issues, such as nonuniformity in which the polarization direction varies due to the variation of devices and instability in which the polarization direction is changed depending on the output and the ambient temperature. Therefore, in the case where such a VCSEL is applied to an optical device with polarization dependence, such as a mirror and a beam splitter, for example, if the VCSEL is used as a light source for a digital copy machine and a printer, there is an issue that the variation in the polarization direction causes a difference in the image location of an image and the output, leading to blur and irregular color.
Therefore, to solve the foregoing issue, a plurality of techniques for providing a polarization control function inside the VCSEL to stabilize the polarization direction in one direction has been reported.
For example, as one of such techniques, there is a technique using a high-angle inclined substrate with a normal line of (311) plane (GaAs inclined substrate). A VCSEL device structured by using such a high-angle inclined substrate has gain property for [−233] direction, and thus the polarization direction of laser light is able to be controlled in this direction. Further, in this case, the polarization ratio of laser light is very high, and therefore this technique is effective for stabilizing the polarization direction of the VCSEL device in one direction.
Further, Japanese Patent Publication No. 2891133 discloses a technique for narrowing the width of one plane in one in-plane direction of a mesa to the degree that light is subject to a diffraction loss on the side face of the mesa, thereby obtaining polarization parallel to the side face.
Further, Japanese Patent Application Publication No. 2001-525995 discloses a technique for forming a discontinuous section in part of the metal contact layer that does not affect the characteristics of laser light emitted from a light emitting aperture, and obtaining polarization parallel to the boundary of the discontinuous section.